1. Field of the Invention
The present invention relates to a yaw rate sensor.
2. Description of Related Art
Micromechanical yaw rate sensors are known from the related art. Such yaw rate sensors are used in different application fields; in the automotive field, for example, they are employed for ESP systems, for roll-over sensing, or for navigation purposes.
Parts of the sensor structure in these yaw rate sensors are actively induced to a drive oscillation along a first direction, which is oriented parallel to a substrate surface, for example. When an outer yaw rate occurs about a detection axis that is oriented perpendicular to the first direction and also parallel to the substrate surface, for example, Coriolis forces come to bear on the oscillating parts of the sensor structure. These Coriolis forces, which may vary periodically with the frequency of the drive oscillation, cause periodic deflections of parts of the sensor structure along a third direction, which is oriented perpendicular to the drive direction and detection axis. For example, the third direction may be oriented perpendicular to the substrate surface. Mounted on the sensor structure are detection means which detect the deflection of the parts of the sensor structure in a capacitive manner via electrodes.
Known yaw rate sensors have only one detection electrode per movable sensor structure, which is fixedly connected to the substrate. This is disadvantageous insofar as the useful capacity between detection electrode and movable sensor structure is low. Furthermore, it precludes a differential detection of the deflection of the movable sensor element using only one stationary detection electrode per movable sensor element.
U.S. Patent Application Publication No. 2008/0168838 A1 describes a yaw rate sensor having a fully differential electrode system, in which a suitably patterned and electrically contacted area in a sensor cap is used as upper counter-electrode. However, despite all manufacturing tolerances, this approach makes it very difficult to adjust the clearance between the movable sensor structure and upper fixed electrode such that it is precisely as large as the clearance between the movable sensor structure and the lower fixed electrode.
Also known from the related art are yaw rate sensors having two coupled movable sensor substructures, which are excitable to a coupled drive oscillation producing an anti-parallel deflection of the movable substructures. Because of the anti-parallel drive oscillations of the two substructures, a yaw rate acting on the yaw rate sensor leads to an anti-parallel deflection of the two substructures. An evaluation of the capacity changes between the movable substructures and the associated fixed electrodes enables a differential detection of the effective yaw rate. One disadvantage of these known yaw rate sensors is their vibration sensitivity and the sensitivity to the excitation of a parallel mode that is difficult to suppress.